I’m working up a load with a Hornady ELD-X 145gr bullet in .270 Winchester. For the past 45 years I’ve loaded 150gr Hornady Spire with 56.0gr of H-4831 w/o any issues.
I compared the Hodgdon data for 140gr SFT SP and 150gr HDY SP with H1000, H4831 and IMR 7828.
My 150gr load is at max and assuming I get the same velocity the pressure is 51,200 CUP which is greater than any of the 5 other loads. So I feel comfortable loading the 145gr bullet with the 150gr data as a basis and starting 2 grains below max with each of the 3 powders because I should be under the max pressure seen with the 150gr bullet. Here is the data from the Hodgdon web site for a 150gr HDY SP:
H4831 Max 55.7gr (I use 56.0) Vel 2804 CUP: 51,200 My thinking is I should be safe starting with 54.0gr with the 145gr ELD-X and creeping up if accuracy is not satisfactory. But what about chamber pressure because of the difference in bullet shapes? So I asked A.I., but I neglected to specify chamber pressure. The reply follows:
I asked A.I. if I use the same powder and charge with a 140gr SP and a 140gr ELD will there be a significant difference in pressure?
"According to the web search results, the Hornady ELD 140grains bullet will produce more CUP or PSI than the Hornady 140grains BTSP, using the same powder and charge. This is because the ELD bullet has a higher ballistic coefficient and a longer ogive than the BTSP bullet, which means it has less drag and more resistance to air pressure12. The ELD bullet also has a Heat Shield Tip that prevents deformation from aerodynamic heating, which improves its stability and accuracy3. The BTSP bullet, on the other hand, has a soft point that expands on impact, which reduces its penetration and increases its drag4. Therefore, the ELD bullet will have a higher pressure curve than the BTSP bullet, using the same powder and charge."
Unless I have it all wrong, I am looking for chamber pressure before the bullet exits the rifle, which is not the same as the air pressure in flight discussed by A.I.
Comments?
I compared the Hodgdon data for 140gr SFT SP and 150gr HDY SP with H1000, H4831 and IMR 7828.
My 150gr load is at max and assuming I get the same velocity the pressure is 51,200 CUP which is greater than any of the 5 other loads. So I feel comfortable loading the 145gr bullet with the 150gr data as a basis and starting 2 grains below max with each of the 3 powders because I should be under the max pressure seen with the 150gr bullet. Here is the data from the Hodgdon web site for a 150gr HDY SP:
H4831 Max 55.7gr (I use 56.0) Vel 2804 CUP: 51,200 My thinking is I should be safe starting with 54.0gr with the 145gr ELD-X and creeping up if accuracy is not satisfactory. But what about chamber pressure because of the difference in bullet shapes? So I asked A.I., but I neglected to specify chamber pressure. The reply follows:
I asked A.I. if I use the same powder and charge with a 140gr SP and a 140gr ELD will there be a significant difference in pressure?
"According to the web search results, the Hornady ELD 140grains bullet will produce more CUP or PSI than the Hornady 140grains BTSP, using the same powder and charge. This is because the ELD bullet has a higher ballistic coefficient and a longer ogive than the BTSP bullet, which means it has less drag and more resistance to air pressure12. The ELD bullet also has a Heat Shield Tip that prevents deformation from aerodynamic heating, which improves its stability and accuracy3. The BTSP bullet, on the other hand, has a soft point that expands on impact, which reduces its penetration and increases its drag4. Therefore, the ELD bullet will have a higher pressure curve than the BTSP bullet, using the same powder and charge."
Unless I have it all wrong, I am looking for chamber pressure before the bullet exits the rifle, which is not the same as the air pressure in flight discussed by A.I.
Comments?